Quantized infrared-optical triple resonance on a single cold barium ion

A single trapped and cooled Ba⁺ ion is irradiated by resonant visible light (493, 650 nm) alternating with light at 1.76 µm which may excite the ion to its² D _5/2 metastable state. The (absence of) visible resonance scattering probes the excitation, tuning spectra of which show vibrational sidebands that characterize the ion's temperature. Observed values as low as 120 µK, one-eighth the Doppler limit, are ascribed to electronic Raman cooling by the visible light. Tuning spectra of the events of stimulated deexcitation indicate ion heating by the IR interaction. The results demonstrate the feasibility of vibrational spectrometry on a single particle that oscillates in a potential well, forming a quasi-molecule.     

Ultrasonic study of solid-phase amorphization and polyamorphism in an H2O-D2O (1: 1) solid solution

The elastic moduli and volume of H₂O-D₂O (1: 1) isotopically mixed ice (solid solution) have been studied at the solid-phase amorphization of normal 1h ice under compression at a temperature of 77 K and at the transition from high-density amorphous ice to low-density amorphous ice with subsequent successive crystallization to cubic (1c) and hexagonal (1h) ice at isobaric (0.05 GPa) heating. Comparison of the results with the respective data for H₂O and D₂O ices indicates that the observed concentration (in the isotopic composition) dependences of the elastic moduli and their derivatives for different phases of ice at isotopic hydrogen substitution in the H₂O, H₂O-D₂O (1: 1), and D₂O chain can be both monotonic and significantly nonmonotonic.     

Muonium in ice

Muonium has been studied in single crystals of H₂O and D₂O. Two-frequency precession in low transverse fields and a single zero-field oscillation indicate a small anisotropy of axial symmetry in the muonium hyperfine interaction. The anisotropy is shown to be the cause of the hitherto unexplained temperature independent contribution to muonium spin relaxation in polycrystalline samples. Relaxation rates for 99 K–263 K are reported for muonium in a single crystal of H₂O. Relaxation is attributed to electron-nuclear dipolar coupling of muonium to lattice protons, modulated by translational diffusion of muonium alongc-axis channels of the ice lattice. A simple model for H and Mu diffusion in ice is investigated.This work was supported by the Natural Sciences and Engineering Research Council of Canada through an Intermediate Energy Physics Project Grant.     

A difference in the electromagnetic properties of D2O and H2O ice revealed by resonance measurements

The dielectric parameters of H₂O and D₂O ice samples were studied by a resonance technique in the region of 6 GHz. The ratio of the resonance curve halfwidths at half maximum was measured for light and heavy ice in the temperature range from 0 to ?130°C. The temperature dependences of the resonance peak asymmetry of the two types of ice are qualitatively different. The ratio of the higher-frequency halfwidths at half maximum to the lower-frequency one plotted versus temperature exhibits a positive slope for light ice and a negative slope for heavy ice. It is suggested that the difference reflects the different quantum statistics of the hydrogen and deuterium nuclei in ice.     

Thermoluminescence study of the amorphisation of hexagonal ice by irradiation at 77 K

This paper reports on a thermoluminescence study of D₂O ice I_h. A sample of hexagonal (I_h) ice is irradiated by a 100 MeV X-ray source at 77 K. The emission spectrum that is measured immediately after the end of the irradiation process has the thermoluminescent behaviour of amorphous ice. The kinetic transition is followed to the stable form, taking place at 85 K. The relaxation time of the transition is of the order of 5 minutes. It is concluded that, due to irradiation, a few outer layers of ice I_h are converted to the low-density amorphous form of ice, which then converts to cubic ice. Although complex to quantify, thermoluminescence appears to be, in the present study, particularly sensitive to the time evolution of irradiated samples.     

Effect of irradiation and pre-ageing temperature on the mechanical properties of Al–Si alloy

Al–1wt.%Si alloy samples in the solid solution state were irradiated with doses of gamma rays up to 1.75 MGy for 2 h in the temperature range from 423 to 553 K. Induced variations in structure, mechanical and electrical properties were traced by suitable techniques. Observed changes in the measured parameters, internal friction Q ^?1, thermal diffusivity D _th, dynamic elastic modulus Y and resistivity, ρ, were explained in terms of the role and mode of interaction of lattice defects in irradiated and thermally treated samples. Composition inhomogeneity and variations in mass distribution in the matrix were also considered. The structure identification of the samples was carried out by using conventional X-ray diffraction techniques and transmission electron microscopy micrographs.     

Anomalously low elastic stability of NaCl-H<Subscript>2</Subscript>O ice at low temperatures

Water-NaCl solid solutions with the salt weight fraction p = 0.0001–0.1000 subjected to high uniaxial compression exhibit elastic instability (similar to the Bridgman explosive effect) in the temperature range 100–260 K. At temperatures from 225 to 260 K, stability threshold P _c (or a critical pressure at which the explosive instability occurs) of these solutions is equal to, or higher than, P _c for pure water ice. However, in the temperature interval 100–225 K, thresholds P _c for the NaCl-water solid solutions with p ≥ 0.001 are anomalously low. The largest drop of P _c (by 15 to 30 times relative to P _c for pure water ice) is observed for low p, 0.001 ≤ p ≤ 0.010. The possible structure of the solid ice solutions in all the temperature ranges mentioned above is analyzed in terms of the percolation theory as applied to elastic networks.     

Optical properties and radiation effects in layered crystals of (CnH2n+nNH3)2MCl4: n = 1, 2, 3; M = Cd,Cu, Mn

Abstract

A new absorption band has been found at 5.10 eV in (C _n H_{2n + 1}NH₃)₂CdCl₄: n = 1, 2, 3 in addition to the absorption bands of CdCl₂ whose electronic structure resembles the former crystals. The energy of the additional peak shifts with temperature by as much as 0.38 eV from 5.10eV at room temperature (RT) to 5.48 eV at liquid nitrogen temperature. This large peak shift is attributed to a structural phase transition between these two temperatures. A new type of electron center has been found in these crystals (M = Cd, Mn; n = 1, 2, 3) irradiated with X-rays at 15 K in addition to the Cl₂ ^?. This shows optical absorption bands (IR bands) in the infrared region of 10 ～ 20 kcm ^?1. The IR bands are assigned to an electron center where an electron is trapped at an ammonium site in the neighborhood of a Cl^? vacancy.     

Properties of 80-MeV oxygen ion irradiated ZnS:Mn nanoparticles and exploitation in nanophotonics

ZnS:Mn nanoparticles of size variation 11–17 nm were synthesized by a simple and inexpensive chemical method and confirmed by transmission electron microscopy (TEM). Presuming electronic energy loss (S _e>S _n, S _n being nuclear energy loss) to be the dominant phenomenon, they were irradiated by 80-MeV energetic oxygen ions with fluence of 10¹¹ to 10¹³ ions/cm². Photoluminescence (PL) spectra revealed three major emission bands ~445 nm, ~582 nm and ~706 nm; which are ascribed to D–A pair transition, Mn emission and surface state led fluorescence activation. The recovery of Mn emission and tunable surface state emission have been observed with ion fluence variation. Infra-red (IR) spectra of irradiated samples show great extent of oscillation with respect to amplitude due to ion fluence variation however, phonon energy (~98 MeV) remains unchanged. The possible applications of these modified properties in nanophotonics are also highlighted.     

Commensurability oscillations and a new phase transition in YBa2Cu3Oy single crystals

Magnetization oscillations due to the commensurability of the vortex and crystal lattice periods in YBa₂Cu₃O_y (y=6.97±0.02) single crystals are investigated using a high angular resolution magnetometer. A sharp peak in the temperature dependence of the oscillation amplitude as well as other features in the behavior of the oscillation amplitude and of the irreversible magnetization are observed at T _f ∼60 K. It is inferred that T _f is the temperature of a transition of the solid vortex state to a smectic phase. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 11, 832–837 (10 June 1999)     

Effect of infrared radiation on the plasticity of solid hydrogen

This paper reports on the first results obtained from the investigation of the effect of IR radiation on the low-temperature (1.8 ≤ T ≤ 4.2 K) plasticity of solid hydrogen. It has been found that, when the samples are exposed to IR radiation, a drastic increment Δɛ_IR of the elongation per unit length ɛ (which was preliminarily achieved under a continuously applied mechanical stress σ = const) occurs without an increase in the temperature of the samples. It has been revealed that the effect observed both in the case of normal hydrogen (n-H₂, 75% o-H₂) and in the case of parahydrogen (p-H₂, ∼0.2% o-H₂) only for a sufficiently high power of the IR radiation source has a threshold character. The reverse deformation of solid hydrogen is observed after the irradiation with a flux of IR photons is completed: the quantity ɛ rapidly decreases to values provided only by the applied load. The appearance of jumps in the increment of deformation Δɛ_IR ⁱ is interpreted as a consequence of the existence of the fundamental IR absorption band for solid hydrogens. It has been established that, depending on the time t of exposure of the samples to IR radiation, the change in the quantity Δɛ_IR ⁱ (t) obeys the logarithmic law, which is characteristic of the dislocation creep and observed in the case of unirradiated hydrogen. It has also been found that, under multiple relatively long-term exposure to IR radiation, the constant α of the logarithmic creep of n-H₂ abruptly decreases, whereas the strength of both the n-H₂ and p-H₂ samples increases significantly, which indicates their explicit hardening (instead of the expected “superplastic” behavior due to the exposure to IR irradiation).     

Reorientations and phase transitions in (Kr)1-x(CH4-nD n ) x

The condensed isotopic modifications of methane, CH₄, CH₂D₂, and CD₄ and their solutions with Kr were investigated using dielectric techniques. The polarizabilities were computed from the permittivities of the pure liquids. Phase diagrams of methane-krypton alloys were deduced in the liquid-solid coexistence region and for the low temperature phases (T<30 K). From the Curielaws, which described the permittivities of the (Kr)_1-x(CH₂D₂)_x mixed crystals, the permanent dioole moment of CH₂D₂ is calculated to be 4 mD. In the octopolar ordered phases of the solid solutions the effective dipole moments are enhanced significantly.     

Refocussing of chemical and paramagnetic shift anisotropies in 2H NMR using the quadrupolar-echo experiment

A simple two-pulse spin-echo experiment is shown to refocus inhomogeneous broadening arising from both chemical and/or paramagnetic shift anisotropy and a first-order I=1 quadrupolar interaction. The method is shown to yield ²H NMR spectra of a paramagnetic solid (CuCl₂ · 2D₂O) and of a non-paramagnetic solid (D₂C₂O₄ · 2D₂O) that are significantly less distorted than those provided by the conventional quadrupolar-echo method. The technique will thus prove useful in studies of motion and dynamics where detailed analysis of the ²H lineshape is performed.     

Isotope effects on the microphase separation of paraffin mixtures

Isotopic sensitivity is reported in both the formation and the above ambient temperature annealing behaviour of lamellar microphases in C₃₀:C₃₆ paraffin solid solutions. The time resolved small angle neutron scattering from a 1:1 C₃₀H₆₂:C₃₆D₇₄ mixture and its complementary pair 1:1 C D :C H has been studied. Upon quenching such mixtures from the melt; the solid solution so formed nucleates spontaneously to a ‘long period’ microphase. The two systems differ in that for 1:1 C₃₀D₆₂:C₃₆H₇₄ there is also strong diffraction at Q = 0·136 A^-1 associated with C₃₆H₇₄ enrichment of the solid solution or a separate phase. Both processes are sensitive to the isotopic composition of the mixture. For both systems the long period scattering from a quenched liquid mixture develops in periods of hours at ambient temperature. Heating the aged microphase structures to temperatures above about 43°C causes them to disappear, but again isotropic sensitivity is noted. It is concluded that the effects are largely kinetic in origin, in agreement with earlier IR studies on intralamellar microaggregation in this system.     

Ion-induced molecular ejection from D2O ice

Studies of molecules ejected from water ice by fast ions provide insight into the electronic relaxation processes and subsequent chemistry occurring in ice at very low temperatures. The ion-induced ejection of D₂O, D₂, and O₂ molecules from thin films of D₂O ice has been measured as a function of the fluence of incident MeV ions at temperatures between 10 and 140 K. For a given beam current, the O₂ yield exhibits initial transients which are slow compared with the prompt ejection of D₂O. We interpret these results as due to the build-up of O₂ in the films following fragmentation of D₂O molecules by incident ions. The fragmens re-form into new molecular species which diffuse to and escape from the surface, aided by subsequent bombardment. The D₂ transient has a prompt component, which we postulate is due to rapid formation during electronic recombination near the surface. A slow component of the D₂ transient is also observed, which may arise through a two-step process similar to that of O₂. Time-of-flight energy spectra of the ejected D₂O molecules have also been measured. Incident ion masses and energies range from those for which nuclear elastic energy deposition dominates (50 keV argon) to those for which electronic energy deposition dominates (1.5 MeV helium). The spectra cannot be described by models typically employed for the sputtering of metals. For instance, the spectra do not have maxima characteristic of the sublimation energy of the solid. In addition, the sputtering yield in the high energy part of the ejection spectrum of D₂O is too large to arise from nuclear elastic energy deposition. It must result instead from relatively energetic non-radiative relaxation of electronic excitation. For incident MeV ions that deposit their energy predominantly in electronic excitation, the low energy part of the D₂O ejection spectrum is greatly enhanced, indicative of a weakly antibinding region formed along an incident particle track. Enhanced ion yields are also found in the collision cascade region which are attributed to electronic processes.     

Optical properties of laser-produced plasmas from Cd and layered crystalline CdAl2Se4 targets

An experimental investigation into emission by plasmas from Cd and crystalline CdAl₂Se₄ targets irradiated with a pulse-periodic YAG: Nd³⁺ laser is presented. The laser operates at a pulse width of 20 ns and provides 1−2×10⁹ W/cm² at the focus. The spectral and time characteristics of the emission are examined. The main findings are as follows: (1) The strongest lines correspond to the transitions from the 6³ S ₁ and 5³ D ₂ levels of Cd I. (2) With the Cd target, the recombination bottlenecks are 5² D _5/2 of Cd II (E _up=20.11 eV) and 8³ D _{1, 3} of Cd I (E _up=8.60–8.65 eV). (3) The average electron temperature outside the core of the plume is 0.64 eV. (4) For the 508.6-nm line of Cd I, the high filling rate of the 6³ S ₁ upper energy level may be related to the rapid recombination of cadmium ions with electrons via the intermediate levels of Cd⁻ at 6.82 and 7.24 eV.     

Effect of γ-irradiation and semiconducting oxide (tio2) on the thermal decomposition of mgc2o4: A comparative study

The simultaneous rising temperature (DTA-TG) technique and the gas evolution method are adopted for studying the thermal decomposition of unirradiated and irradiated MgC₂O₄ and MgC₂O₄ + TiO₂ mixtures. The data are applied to theories of different solid state reaction models and the best fit is obtained for the Avrami-Erofeev mechanism (n=2) suggesting that both the nucleation and growth processes occur at the reactant product interface in a two dimensional chain branching manner. Low irradiation doses decrease the rate of reaction remarkably whereas the reverse phenomenon takes place at higher doses. The n-type semiconducting oxide, TiO₂ (5-40 mol%) enhances the rate of decomposition which increases with increasing concentration of the catalyst. The influence of n -irradiation is explained in the light of defects, dislocations and electron-hole (e^?, h⁺) pairs generated in the lattice, whereas the influence of TiO₂ is understood on the basis of electron transfer process involved in the reaction.     

Investigation of the interface trap density and series resistance of a high-k HfO2-based MOS capacitor: before and after 50 MeV Li3+ ion irradiation

This is the first investigation on the effects of 50 MeV Li³⁺ ions on interface trap density (D _it) and series resistance (R _s), which reveal the improvement of the dielectric properties of RF-sputtered HfO₂-metal oxide semiconductor (MOS) capacitors. The samples were irradiated and characterized at room temperature. The D _it and R _s were determined from the capacitance–voltage (C–V) and conduction–voltage (G–V) characteristics at 1 MHz. The measured capacitance and conductance were corrected for series resistance. It is found that the series resistance of Al/HfO₂/p? Si MOS capacitors increases with ion fluence, calculated at a strong accumulation region before and after irradiation. The interface state density of MOS devices before and after irradiation is found to decrease with increasing ion fluence.     

High pressure X-ray diffraction and Raman spectroscopic studies of the phase change of D2O ice VII at approximately 11 GPa

High pressure experiments were performed on D₂O ice VII using a diamond anvil cell in a pressure range of 2.0–60 GPa at room temperature. In situ X-ray diffractometry revealed that the structure changed from cubic to a low symmetry phase at approximately 11 GPa, based on the observed splitting of the cubic structure's diffraction lines. Heating treatments were added for the samples to reduce the effect of non-hydrostatic stress. After heating, splitting diffraction lines became sharp and the splitting was clearly retained. Although symmetry and structure of the transformed phase have not been determined, change in volumes vs. pressure was calculated, assuming that the low-symmetry phase had a tetragonal structure. The bulk modulus calculated for the low-symmetry phase was slightly larger than that for the cubic structure. In Raman spectroscopy, the squared vibrational frequencies of ν₁ (A_1g), as a function of pressure, showed a clear change in the slope at 11–13 GPa. The full width at half maxima of the O-D modes decreased with increasing pressure, reaching a minimum at approximately 11 GPa, and increased again above 11 GPa. These results evidently support the existence of phase change at approximately 11 GPa for D₂O ice VII.     

The coil → blob transition in atactic poly(styrene) films

The structure of atactic poly(styrene) in films prepared from chloroform solutions was studied by small-angle X-ray scattering and electron microscopy. It was shown that the density fluctuations in films corresponding to dilute poly(styrene) solutions are associated with the aggregates of particles with the radius R ₀ close to the hydrodynamic radius of the coil. The value of R ₀ in the films decreases with an increase in the poly(styrene) concentration due to the coil entanglement and the blob formation. The coil (its fractal dimension is D = 2) → blob (D = 3) transition leads to an increase in the density and glass transition temperature of films, which is caused by enhancing interchain and intrachain interactions of segments in the solid state of atactic poly(styrene).